Energy and economic analysis of an ICE-based variable speed-operated micro-cogenerator Flavio Caresana a,⇑ , Caterina Brandoni b , Petro Feliciotti c , Carlo Maria Bartolini a a Università Politecnica delle Marche, Dipartimento di Energetica, Via Brecce Bianche, Ancona (AN) 60100, Italy b Università Telematica e-Campus, Ingegneria Energetica, Via Isimbardi 10, Novedrate (CO) 22060, Italy c Università Politecnica delle Marche, Dipartimento di Ingegneria Informatica, Gestionale e dell’Automazione, Via Brecce Bianche, Ancona (AN) 60100, Italy article info Article history: Received 2 September 2009 Received in revised form 6 August 2010 Accepted 16 August 2010 Available online 24 September 2010 Keywords: Distributed generation Cogeneration Micro-CHP plant Internal Combustion Engine Variable speed Economic feasibility abstract Micro-combined heat and power (CHP) systems are a key resource to meet the EUCO 2 reduction agreed in the Kyoto Protocol. In the near future they are likely to spread significantly through applications in the residential and service sectors, since they can provide considerably higher primary energy efficiencies than plants generating electricity and heat separately. A 28 kW e natural gas, automotive-derived internal combustion engine CHP system was modeled with a view to comparing constant and variable speed operation modes. Besides their energy performances, the paper addresses the major factors involved in their economic evaluation and describes a method to assess their economic feasibility. Typical residential and service sector applications were chosen as test cases and the results discussed in terms of energy per- formances and of profitability. They showed that interesting savings can be obtained with respect to sep- arate generation, and that they are higher for the household application in variable speed operating conditions. In fact the plant’s energy performance is greatly enhanced by the possibility, for any given power, to regulate the engine’s rotational speed. From the economic viewpoint, despite the higher initial cost of the variable speed concept, the system involves a shorter pay-back period and ensures greater profit. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The European Community has set a target of 18% for combined heat and power (CHP) generation to meet the EUCO 2 reduction agreed in the Kyoto Protocol [1]. The Italian legislator has recog- nized cogeneration as one of the most efficient energy-saving tech- nologies [2] and has granted fiscal and administrative advantages for the development and installation of micro-cogeneration sys- tems (units producing < 50 kW e ), which have the added benefit of contributing to decarbonizing the energy supply [3]. Albeit currently underexploited, mainly due to their poor com- petitiveness [4], micro-CHP systems are likely to spread signifi- cantly in the near future, mainly in the household and service sectors [5], where their primary energy efficiency greatly exceeds that of plants generating electricity and heat separately. In this re- spect their electric efficiency and flexibility will help them meet the ever stricter regulatory parameters [6] and will be key assets in view of their large-scale application in a liberalized market, once the micro-CHP concept has been proved to be feasible and compet- itive [7,8]. The most common small-scale natural gas cogeneration sys- tems are based on internal combustion engines (ICE); in recent years microturbine generators [9–11] have also entered the mar- ket, and even Stirling engines are being considered for high-tem- perature thermal demand applications [12]. Besides a relatively high electric efficiency, valued features of ICE-based cogenerators are low initial investment and, especially, great reliability, a typical aspect of a mature technologies [13]. At the environmental levels key areas of concern are NO x emis- sions (involved in local/regional air quality), greenhouse gas emis- sions (involved in climate change), and noise. In fact, the emission rate from natural gas-fuelled distributed generation (DG) plants is higher than the ‘best available’ fossil-fired central generation plants, a combined-cycle gas turbine with advanced emission con- trol. This drawback involves severe limitations for DG in areas where NO x emission caps are closely enforced. The carbon dioxide (CO 2 ) emissions of DG plants are also higher than those of new combined cycles, except CHP systems, as shown in this paper. However, incentives can be designed to encourage DG operators to reduce emissions; for instance, schemes like carbon emission trading would encourage them to design and operate their facili- ties in ways that minimize emissions of greenhouse gases. Finally, since these plants are being installed near populated areas, acous- tic insulation is required to avoid affecting nearby residents [14]. 0306-2619/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2010.08.016 ⇑ Corresponding author. Tel.: +39 0712204765; fax: +39 0712204770. E-mail address: f.caresana@univpm.it (F. Caresana). Applied Energy 88 (2011) 659–671 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy